1. Field of the Invention
The present invention relates to a method for removing a resist pattern that is formed in a photolithography process and a method for manufacturing a semiconductor device by using the method for removing a resist pattern. Specifically, the present invention relates to the technique for removing a resist pattern after an etching process or a doping process.
2. Description of the Related Arts
In recent years, active matrix liquid crystal display devices having circuits including TFTs are applied to the display screens of personal computers and television sets, and such various products are distributed in the market. In addition, active matrix EL display devices that are of the self-luminous type without backlights are developed for productization.
In the manufacture of a display device such as an active matrix liquid crystal display device or an EL display device, similarly to the case of an LSI (Large Scale Integrated Circuit) fabricating process, a thin film depositing process such as a CVD process, a photolithography process, an etching process, and a resist removing process are repeatedly performed to form a fine device pattern. The photolithography process is a process for forming a resist pattern which becomes a base for the device pattern, the etching process is a process for forming the device pattern for etching an underlying-layer film by using the resist pattern as a mask, and the resist removing process is a process for removing an unnecessary resist pattern after the etching process.
The above-described photolithography process is the process for forming a resist pattern which becomes a mask in etching, and in the process of manufacturing the display device, a diazonaphthoquinone (hereinafter abbreviated to DNQ)-novolac resin type of positive resist is generally used as a resist material. For an aligner used in the photolithography process, a 1:1 projection aligner (1:1 projection exposure system) which uses multiple-wavelength light including g-line (436 nm), h-line (405 nm) and i-line (365 nm) which are spectral light of an ultra high pressure mercury lamp, or a 1:1 projection aligner using single-wavelength light (abbr. a 1:1 stepper) of g-line or i-line of an ultra high pressure mercury lamp is used. With regard to specific processes of the photolithography process, the case where the 1:1 projection aligner of multiple-wavelength light is used is different from the case where the 1:1 projection aligner of single-wavelength light is used.
The photolithography process in the case where the 1:1 projection aligner of multiple-wavelength light is used includes a series of steps: resist coating→prebake (approximately at 100° C.)→exposure→development→postbake (approximately at 120° C.). The photolithography process in the case where the 1:1 projection aligner of single-wavelength light is used includes a series of steps: resist coating→prebake (approximately at 100° C.)→exposure→bake after exposure (Post Exposure Bake, hereinafter, PEB) (approximately at 120° C.)→development→postbake (approximately at 120° C.).
A resist pattern formed in the photolithography process serves as a mask in dry etching or wet etching, and it is necessary to remove the unnecessary resist pattern after the etching process. Thus, a resist removing process which includes an ashing process and a resist stripping treatment is performed for the purpose of removing such unnecessary resist pattern. The ashing process is the step of decomposing a resist pattern into a carbon dioxide gas by means of oxygen plasma. The resist stripping treatment is the step of dipping a substrate after an ashing process into an organic resist stripper adjusted to a predetermined temperature and dissolving and removing a resist pattern by using the dissolution action of the resist stripper.
However, in the resist removing process, it is known that a resist pattern after doping or dry etching becomes difficult to remove. For example, when a resist pattern over a substrate passes through a dry etching process, the reaction of polymers which constitute a resist pattern with an etching gas and the cross-linking reaction between the polymers proceed and a deteriorated layer difficult to remove is produced over the surface of the resist pattern. The deteriorated layer is stable and is difficult to remove by ashing. The speed of ashing is improved by adding a predetermined ratio of hydrogen or nitrogen to oxygen which is an ashing gas. Alternatively, the speed of ashing is also improved by adding a halogen gas such as CF4 to oxygen which is an ashing gas. However, since there is a problem of an etching-damage of a base material due to the selectivity of the resist pattern to the base material, the applicable scope of the ashing process is restricted. Further, there is also a problem of a corrosion or etching of a base material caused by using a resist stripper having strong removing ability in the resist stripping treatment after an ashing process.